Implantable medical devices, such as implantable cardioverter defibrillators, are used in a variety of therapeutic applications. In some implantable medical devices, a pulse generator and a medical lead, each having electrodes, are used together to provide electro stimulation therapy in the form of electrical pulses delivered to a tissue site within a patient. In some medical devices, the electrodes used to delivery therapy may also be used to sense conditions within the body that indicate the effectiveness of the therapy or indicate a need for additional therapy.
In some implantable medical devices, the delivery of therapy in the form of an electrical pulse may interfere with the ability of the device to subsequently sense the effectiveness of the therapy. In some implantable medical devices, such as an implantable cardioverter defibrillator, the electrical pulse may be delivered at a relatively high voltage, such as 1,000 volts (V), to provide effective therapy. In other devices, such as a subcutaneous implantable cardioverter defibrillator, the electrical pulse may be delivered at an even higher voltage, such as 3,000 V. The electrical pulse creates an electrical charge in and around the target tissue site. Once therapy is delivered, the electrical charge begins to dissipate. Until the charge dissipates, it may interfere with and prevent detection of conditions within the body that indicate the effectiveness of the therapy. At higher voltages, the electrical charge takes longer to dissipate. The delay between delivery of an electrical pulse and the time at which enough of the electrical charge has dissipated that the effectiveness of the therapy can be sensed is called the post-shock recovery time.
In some cases, a post-shock recovery time may be an important factor in the effective delivery of therapy. In cases where an initial electrical pulse does not result in a desired outcome and an additional electrical pulse may be required, a long post-shock recovery time will delay the additional therapy. In some cases, such a delay may reduce the overall effectiveness of the therapy. One way to dissipate the electrical charge more quickly, improve sensing capabilities, and reduce the post-shock recovery time is to decrease the impedance of at least one of the electrodes.